The invention relates to micro-switches for use in various tools, such as downhole well tools.
In forming a well, many different types of operations may be performed, including drilling, logging, completion, and production operations. Various different types of devices are used to perform the desired operations. Examples of such devices include perforating guns to perform perforating operations, flow control devices to control fluid flow (injection or production), packers to isolate different regions of the well, and other devices.
The activating mechanisms to activate such devices may include mechanical, hydraulic, and electrical activating mechanisms. To electrically activate a downhole device, a power source is connected to the downhole device. This is typically accomplished by using switches, either at the surface or in a downhole module. The switch is initially open to isolate the power source from the downhole device. When activation is desired, the switch is closed to provide electrical power to the downhole device.
In wellbore applications, one type of switch is made from a gas discharge tube that is either a triggered type of over-voltage type switch. A triggered-type switch employs an external stimulus to close the switch or to activate it. An over-voltage switch is activated whenever the voltage level on one side of the switch exceeds a threshold value.
Some switches employ a gas tube having an electrode at each end. In order to make the switch conduct, either a trigger voltage is applied to a third internal grid or anode, or the switch is forced into conduction as a result of an over-voltage condition. Because the typical gas tube discharge switch is arranged in a tubular geometry, it is usually associated with a relatively high inductance. Also, the tubular shape of a gas tube does not allow convenient reduction of the overall size of a switch. Additionally, it may be difficult to integrate the gas tube switch with other components.
Another type of switch includes an explosive shock switch. The shock switch is constructed using a flat flexible cable having a top conductor layer, a center insulator layer, and a bottom conductor layer. A small explosive may be detonated on the top layer causing the insulator layer to form a conductive ionization path between the two conductor layers. One variation of this is a “thumb-tack” switch in which a sharp metal pin is used to punch through the insulator layer to electrically connect the top conductive layer to the bottom conductive layer.
The explosive shock switch offers a low inductance switch but an explosive pellet must ignite to trigger the switch. The thumbtack switch is similar to the explosive switch but it may not be reliable. Thus, a need continues to exist for switches having improved reliability and triggering characteristics.